The present invention relates to a control apparatus for a linear motor suitable for use in optical head access or the like in an optical disk drive unit.
A conventional high-precision positioning control apparatus for a linear motor is described in Japanese Patent Disclosure (Kokai) No. 60-134793. The summary of this conventional apparatus will be described with reference to FIG. 4. A target position signal is input to the positive input of adder 3 and its negative input receives a present position signal from position detector 2. The present position signal is used to detect a present position of a moving piece of linear motor 1. Adder 3 calculates a position deviation. The position deviation signal output from adder 3 is input to the positive input of adder 5, and its negative input receives a speed feedback signal. The speed feedback signal is obtained from speed detector 4 for detecting the present speed of the moving piece of linear motor 1. Adder 5 calculates a deviation between the input signals, and its output is amplified with a gain K1 or K2 by amplifier 6 or 7. Amplifier 6 or 7 is selected by switch 9 controlled in response to an output from speed level detector 8. The signal from selected amplifier 6 or 7 is input to driver circuit 10 for linear motor 1. Linear motor 1 is controlled on the basis of the output signal from driver circuit 10, such that the moving piece of motor 1 reaches the target position.
In the conventional apparatus described above, the gain (K1, K2) is switched only by the result obtained by detecting the present speed level. Then, an abrupt change occurs in movement of linear motor 1 upon gain switching. For example, in an optical pickup linear motor in a CD player for vehicle mounting, when the linear motor is inclined with respect to the earth, a gravity component adversely affects the thrust of the linear motor. As a result, when the inclination angle of the linear motor with respect to the earth is increased, the position etc., of the moving piece of the linear motor cannot be often controlled.